In recent years, a large amount of silica is incorporated in a tread rubber of a pneumatic tire. Silica has a merit that it reduces rolling resistance and enhances wet grip performance of the tire. However, since silica has a poor conductivity, electric resistance of the tread rubber is increased. Such a tire tends to accumulate static electricity in a vehicle and to cause radio interference such as a radio noise.
In order to prevent the accumulation of static electricity in a vehicle, for example, a tread rubber (a) as shown in FIG. 25 is proposed. The tread rubber (a) has a double layer structure including a base portion (c) located on a radially inner side and a cap portion (b) disposed radially outward of the base portion. To enhance a driving performance and the like of the tire, the base portion (c) and the cap portion (b) are made of a non-conductive rubber containing a large amount of silica. Moreover, the base portion (c) and the cap portion (b) are each divided into right and left parts, and a through-terminal portion (d) made of, for example, a conductive rubber containing a large amount of carbon is disposed between them.
The through-terminal portion (d) continuously extends in the tire circumferential direction, and a radially outer surface of the through-terminal portion (d) constitutes a part of a ground-contacting surface (g). A radially inner surface of the through-terminal portion (d) is connected to a tread reinforcing cord layer (f), such as a belt layer, which is electrically conducted with a rim (not shown) through a sidewall rubber or the like when the tire is mounted on the rim. Such a tread rubber (a) can discharge static electricity accumulated in a vehicle to a road through the rim, the sidewall rubber, the tread reinforcing cord layer (f), and the through-terminal portion (d).
However, in the tread rubber (a) shown in FIG. 25, the base portion (c) is completely divided into the right and left sides. In other words, in the tread rubber (a) described above, a region where the base portion (c) having a low rolling resistance is not present is continuously formed in the circumferential direction of the tire. In such a tread rubber (a), an effect for reducing the rolling resistance of the tire cannot be expected sufficiently.
In a case where the base portion (c) is completely divided into the right and left sides, a pasting position of the base portion (c) is prone to be deviated when the tread rubber (a) is formed. This may deteriorate uniformity of the tire. The following publications show related arts:    Patent Literature 1: JP-A-9-71112    Patent Literature 2: JP-A-2000-94542